1. Field of the Invention
This invention relates to an automatic car-speed controller used for controlling the travelling speed of a motor vehicle at a set point automatically.
2. Description of the Prior Art
Heretofore, there have been many types of such automatic car-speed controllers. Among them, for example, there has been an automatic car-speed controller comprising a car-speed sensor for outputting car-speed data proportional to an actual car-speed, a command switch for outputting a cruise command signal, an actuator for driving a throttle by rotation of a driving motor through an electromagnetic clutch, a motor-driving circuit for rotating the driving motor of said actuator in the forward and reverse directions and a clutch-driving circuit for switching said electromagnetic clutch on or off, and provided with a car-speed memorizing means for memorizing the car-speed data of said car-speed sensor in response to an operation (ON-operation or OFF-operation) of said command switch and a control means for controlling said respective driving circuits in accordance with difference between actual car-speed and memorized car-speed in a microcomputer.
In said automatic car-speed controller, by operating a setting switch of the command switch, the car-speed at the time of the operation is memorized by the car-speed memorizing means in the microcomputer. The control means actuates the motor-driving circuit and the clutch-driving circuit according to the difference between actual car-speed and memorized car-speed, thereby making the electromagnetic clutch of the actuator into an excited state and driving the throttle in the opening or closing direction by the rotation of the driving motor of the actuator through said electromagnetic clutch, the actual car-speed being controlled into said memorized car-speed so as to travel at a constant speed. Upon operating a brake pedal at the time of traveling at the constant speed, the car-speed control is cancelled by inputting a cancel signal generated according to the operation of said brake pedal into the control means in the microcomputer, the motor-driving circuit stops the rotation of the driving motor in the actuator according to a cancel signal from the control means and the electromagnetic clutch is made into a non-excited state by the clutch-driving circuit, whereby the system is cancelled.
However, in the conventional automatic car-speed controller described above, it is impossible to declare that there is not any possibility that some abnormality may arise in the microcomputer from inconceivable factors such as a remarkably large overcurrent, unforeseen damage caused by radio waves, and the like during the car-speed controlling operation. Therefore, an abnormality-detecting circuit is provided for cancelling the system by detecting the abnormality of the microcomputer and making the electromagnetic clutch into the non-excited state. However, the motor vehicle may be accelerated if the operation of the electromagnetic clutch is abnormal during disconnection due to trouble such as fusion bonding, for example, and the driving motor of the actuator is driven in the opening direction of the throttle as a result of the microcomputer trouble. When the driver notices the abnormality of the car-speed control and operates the brake pedal, the stopping force is applied on the vehicle, however that may be a problem in that the vehicle is accelerated again upon discontinuing the brake operation because the connection of said electromagnetic clutch is not interrupted.
In the automatic car-speed controller as described above, said actuator is provided with two limit switches for detecting the full-opened position and the full-closed position of the throttle respectively, and is so designed as to prevent the driving motor from burning out by making respective limit switches into an open state when said throttle arrives at the full-opened position or the full-closed position.
In the aforementioned conventional automatic car-speed controller, when the throttle stays at the full-closed position, it is impossible to confirm the conductivity of the limit switch for detecting the full-closed position of the throttle because said limit switch is in the open state when the throttle is at the full-closed position. Therefore, the conductivity of said limit switch is confirmed at the state in which the throttle is driven temporarily in the opening direction by the control means through the motor-driving circuit. However, there is a problem in that it is impossible to drive the throttle in the closing direction by the actuator when said limit switch does not come into the conductive state due to some trouble.